NiSi crystal structure, site preference, and partitioning behavior of palladium in NiSi(Pd)/Si(100) thin films: Experiments and calculations

Abstract

The crystal structure of a NiSi thin-film on a Si substrate and Pd site-substitution in NiSi and the partitioning behavior of Pd for NiSi(Pd)/Si(100) are investigated by x-ray diffraction (XRD), first-principles calculations, and atom-probe tomography (APT). The NiSi layer is a distorted orthorhombic structure from XRD patterns via experiments and calculations. We find that Pd has a strong driving force, 0.72 eV atom À1 , for partitioning from Si into the orthorhombic NiSi layer. The calculated substitutional energies of Pd in NiSi indicate that Pd has a strong preference for Ni sublattice-sites, which is in agreement with concentration profiles determined by APT. Transition-metal silicide thin-films are extensively studied and widely used due to their low-resistivity in micro-and nano-electronic devices. 1-6 NiSi has been used for contact applications in the source, drain, and gate regions of complementary metal-oxide-semiconductor (CMOS) field-effect transistors, since 65 nm technology node. Fully silicided (FUSI) NiSi gates manufactured by a two-step self-aligned (salicide) process are also being actively studied. 8 NiSi has a lower temperature of formation, lower resistivity in narrow dimensions, and lower Si consumption, making it preferable to TiSi 2 and CoSi 2 contacts. Laser-assisted local-electrode atom-probe (LEAP) tomography utilized a pulsed laser to dissect specimens on an atom-by-atom basis at 40 K under ultrahigh vacuum conditions (<10 À10 Torr). A pulsed picosecond laser (wavelength ¼ 532 nm) operating at 250 kHz, 0.5 nJ pulse À1 , was employed to dissect a specimen with a 10 nm Ni(Pd) layer and a micro-tip length of 500 nm. LEAP tomographic samples were fabricated using a FEI Nova dual-beam focused ion-beam (FIB) microscope employing the lift-out technique. The electronic structures of pure NiSi and the sublattice site-preference of the dopant, Pd, were studied using firstprinciples calculations: full-electron (WIEN2K) (Ref. 16) and pseudo-potential calculations (VASP) (Refs. 17, 18) were utilized. Full-electron self-consistent calculations of the electronic structure and optical properties based on the scalar relativistic full-potential linearized augmented plane-wave a